Hot-Carrier Stressing of NPN Polysilicon Emitter Bipolar Transistors Incorporating Fluorine

The effects of fluorine on the hot-carrier induced degradation in low-thermal-budget polysilicon-emitter NPN bipolar transistors have been examined. Forward Gummel plots, base-emitter (BE) diode characteristics, and stress currents were measured during reverse BE bias stress. Fluorinated devices behave similarly under stress to nonfluorinated devices retaining the initial improvement observed in the forward-bias base current, which is due to suppression of recombination in the BE junction depletion regions at the oxide/silicon interface. The benefits of fluorination, and particularly the reduction in base current in fluorinated devices, appear to be robust—that is, there is no evidence that the defects passivated by fluorine are reactivated during stressing, or that fluorination introduces additional defects that are activated under stressing.